Actually that just highlights the massive amount of space you must be leaving open for them. Big dudes like that have no business getting that if you're at all tight.

Anyway, all the counters have already been mentioned leaving this:
quit playing footsie

Pfft...rip their big ole foot off. So I havent seen any gimmicky moves in here, so here ya go: If your right arm is trapped betwixt his legs reach under and around his right leg keeping your wrist tight to the bend in his hip. Gable grip your hands together and walk towards his head while you drop your hips to the floor and squeezer with your hands.

Now with the gimicky part over, this is useful to actually transition to a kneebar when their legs pop open.

Hey guys, I have a technique related question. I did some searching, but I'm not too sure on the nomenclature, and I didn't find anything anyway.

Essentially, I'm in sidemount. I have one arm close to his head, and for the sake of description, one arm near his legs. He clamps the near-leg arm with his legs. Now, he pushes my head into this, trapping my head and arm in betwixt his head, just like a triangle. Except that I'm facing the opposite way than I would be in a normal triangle. I don't know what it's called; I had guessed reverse triangle.

inverted, not reverse. reverse is from the back. inverted is facing the feet.

I would actually prefer to try circling slightly towards the legs and popping the head out using the free hand on their hooking leg, the far one from you, before they lock it in properly but that's because:

1) I'm fighitng fellow Judoka so the chances of them finishing it are lower than of BJJ guys finishing it anyway so I can chance this

2) I'm fighitng Judoka who aren't that experienced (Max 4 years)

3) The sole reason that I perform this move is to get people to circle towards my head so I can try and get some of their weight on me then bridge and roll them over

And besides which I would still use the other escapes listed above if that failed or if I didn't initiate it early enough anyway.